Treatment of brass



3,046,166 ATMENT F BRASS Robert F. Hartmann, St. Louis County, Mo., assignor to Olin Mathieson Chemical Corporation, East Alton, Ill., a corporation of Virginia No Drawing. Filed July 1, 1959, Ser. No. 824,197 12 Claims. (Cl. 148-115) This invention relates to brasses and more particularly to the treatment of copper-zinc and copper-nickel-zinc alloys.

The brasses to which this invention is directed are those containing copper, nickel and/or zinc in major amounts, but however, do not exclude minor amounts of additional metals, either as impurities or as metals intentionally added to impart modified properties to the alloy. For example, either the copper-zinc alloys or the coppernickel-zinc alloys may contain small amounts of lead, tin, manganese and/or metals added in small amounts to modify the properties thereof. Typical of the alloys contemplated in this invention are the brasses commonly known as cartridge brass having the following compositions: 68.5 to 71.5% copper, 0.075% maximum lead, 0.06% maximum iron, 0.15% maximum other impurities and balance zinc. Typical of the coppcr-nickel-zinc alloys are those having the following compositions: 53.5% to 73.5% maximum copper, 17.0 to 19.5% maximum nickel, 0.50% maximum manganese, 0.25% maximum iron, 0.10% maximum lead with the remainder zinc. These last said alloy compositions are generally referred to as 18% nickel silver alloys.

In the fabrication of the above alloys it has been customary heretofore to subject these metals to cold working operations which result in distortion and straining of the grain structure to a point resulting in a decrease in ductility where further working cannot be done economically or without structural damage to the metal. To restore ductility for additional cold working, the metal is heated to above its recrystallization temperature to remove the eifects of cold Working. At the recrystallization temperature, the distorted grain fragments coalesce to form a new recrystallized structure. During recrystallization the formation of new grains alters the physical properties of the metal. With the growth of the grains, by coalescence, the tensile strength, elastic limits and hardness decreases while elongation and reduction in area increases. Correlation of strength to grain size is limited by the conventional schedules heretofore employed for processing the copper-base alloys to which this invention is directed. However, in many applications, for example in springs, there is a need for higher strengths in conjunction with finer grain sizes.

Accordingly, it is an object of this invention to provide a novel process for working copper-base alloys to obtain higher mechanical and physical properties.

Another object of this invention is to provide a novel process for working copper-base alloys having higher strengths in conjunction with a finer grain structure.

Still another object of this invention is to provide a novel process for working metals having higher ductility to strength ratio.

In accordance with this invention, the above objects and other objects may be accomplished by providing a treatment for Working the aforesaid copper-based alloys by a method consisting of a succession of cold rolling operations to reduce the metal to the desired size and shape, each of which is followed by heat treatment at temperatures below the recrystallization temperature of the alloy so as to stress relieve the alloy. Each of the cold rolling steps will involve a reduction in the thickness of the alloy of at least 50% and preferably 70%. More specifically, the invention contemplates consecutive treatseries is employed and limited to define a two stage- 3,046,166 Patented July 24, 1962 ice ments of the alloy involving at least one series consistingof the aforesaid cold working operation and a heat treating operation at temperatures below the recrystallization of the alloy. Generally, the heat treatment will be at 300 C. for the nickel silver alloy, and 200 C. for copperzinc alloys. For purposes of this application the term operation consisting of a single cold Working operation followed by a single stress-relief annealing operation at temperatures below the recrystallization temperatures of the alloy processed so as to prevent any grain growth in the alloy.

Following the penultimate anneal at below the recrystallization temperatures the alloy is again cold worked and further processed to the specific physical and mechanical properties desired in the ultimately processed alloy. Generally, this cold working operation Will also involve at least 50% reduction.

Following this last said cold working, of the alloy, it is essentially that the subsequent heat treatments, final anneals, do not permit growth of the grains, of the alloy, above a maximum of 0.005 millimeter. Such final anneals may then be followed by rolling to a finish gauge, or a cold rolling reduction followed by still an additional anneal either at, below or slightly above recrystallization temperatures without preventing the growth of the grains above a maximum grain size larger than 0.001 millimeter. Preferably, the total reductions imparted by all of the cold working operations will be in the range between and 97%.

The total cold reduction generally, for economic con-\ siderations, will involve three stages, each involving at least 50% and usually 70%, to the alloy thickness entering each cold working operation, to give a total reduction between 95 to 97%, from scalp gauge to finish gauge. These heavy reductions severly fragment the grain of the alloy resulting in finer grain structures both after rolling and after the stress-relief anneals. The combined cold working operations are in effect a very large single reduction which is interrupted for a stress-relief annealing heat treatment. Any number of series of cold working operations and stress-relief anneals may be employed and are contemplated within the scope of this invention with the total reduction preferably between 95 and 97%. Although stress-relief annealed temperatures are referred to broadly, they are readily obtained by reference to annealing graphs available in standard reference works, such as the Metals Handbook published by the American Society for Metals. For purposes of this application, a stress-relief anneal is employed in the conventional and accepted sense to involve only a complete relief of internal stresses and not to cause nucleation of new grains.

The use of a stress-relief anneal between cold working operations is essential for purposes of this invention. The. stress relief anneal employed in this invention increases the strength of the alloy without destroying the effects of the cold working whereas, conventionally, the normal function of an annealing operation is to prepare the metal for further mechanical working by heat treating the metal above the recrystallization temperature so as to destroy the effects of the cold deformation and thus, soften the metal and greatly increase its capacity for further cold working. Although the deformation is contemplated to be obtained in this specification by means of cold rolling operations, as is obvious it may also include other means, such as by drawing through dies and other cold working methods.

More specifically a 0.470 inch thick sheet of cartridge brass was given a R.G.R. (Ready to ,Get Ready) cold reduction to 0.141 followed by an anneal for one hour at 200 C. The rolling was then continued to effect R.F. (Ready to Finish) reduction from 0.14" to 0.039" in sesame thickness and against stress-relief annealed for one hour at 200 C. The above described treatment for the cartridge brass consists of two series of treatments with each searies consisting of a cold working operation followed by a stress-relief anneal. Subsequent to the last stress-relief anneal, the metal, in accordance with this invention, may be further treated by cold working to effect a final reduction to 0.014" and again annealed at 200 C. for one hour at a temperature so that the last two operations are in effect one additional series of operations which as defined consists of a cold working and a stress-relief anneal. The final stress-relief anneal will give no recrystallization, an ultimate strength of 123,000 p.s.i. (pounds per square inch) and a yield strength of 99,000 p.s.i.

A modification of the treatment to which the alloy is submitted may involve only one series of operations consisting of R.G.R. reduction from 0.470" to 0.141" followed by stress-relief anneal for one hour at 200 C. Following the anneal, the alloy is given a R.F. reduction from 0.141" to 0.039" followed by RF. annealing for one hour at 375 C. which provides a grain size of 0.002 millimeter well below the maximum size of 0.005 millimeter. Following this anneal, the alloy was given a finish reduction from 0.039" to 0.0 14" followed by a stress-relief finish anneal at 200 C. for one hour. The resultant process alloy was found to have no recrystallized grains.

The results of the above processes to which the cartridge brass was submited are tabulated below:

Ultimate Yield Grain Size, Step Condition Strength, Strength, Millimeters p.s.i. p.s.i.

1 R.G.R. Cold Rolling from 96, 000 75, 000

0.047 to 0.141. 2 R.G.R. Anneal, 200 0., 102, 000 86,000 No recrystal- 1 hr. lization. 3 R.F. Cold Rolling, 0.141 109,000 89, 000

to 0.039. 4 R.F. Anneal, 200 0., 1 hr. 119,000 101, 000 Do. 6..-..." Finish Cold Rolling, 106,000 90,000

0.039 to 0.014. 6 Anneal, 200 0., 123, 000 99,000 Do.

The above data illustrates the process of this invention with all the anneals at 200 C. (stress-relief anneals).

The above data illustrates a process as outlined in this invention with the first anneal at 200 C., the second anneal slightly above the recrystallization temperatures and the final anneal at 200 C.

The last modification discussed above and depicted in the second table illustrates the processing of cartridge brass, to finish, within the scope of this invention following only one series of operations consisting of cold working followed by a stress-relief anneal. Other modifications of the treatment of cartridge brass within the scope of this invention are exemplified in the following treatments which involve two series of operations wherein each series consists of cold reductions each followed by a stress-relief anneal. Subsequent to the last annealing, the cartridge brass is again given a cold reduction followed by an anneal at 250 C. This process is illustrated in the tabulation immediately below wherein a grain size of 0.001 millimeter was obtained in conjunction with an ultimate strength of 78,000 and a yield strength of 55,000.

Ultimate Elong., Yield Grain Step Condition Strength, Percent Strength, Size,

p.s.i. in 2 p.s.i. Millimeters 1 R.G.R. Cold 96, 000 75,000

Tipping, .470" to R.G.R. Anneal, 102,000 86,000 No recrys- 200 C. for 1 hr. tallization. R.F. Cold Rolling, 109,000 89,000

.141 to .030. RF. Annealing at 119,000 101,000 Do.

200 C. for 1 hr. Finish Cold Rolling, 106,000 90, 000

.039 to .014. Finish Anneal, 250 78,000 20 55,000 0.001.

C. at 1 hr.

If in the last described modification the RF. anneal is just above the recrystallization temperature without permitting the maximum grain size to exceed 0.005 milli meter, the following fine grain material was obtained as set forth in the following tabulation:

Ultimate Elong, Yield Grain Step Condition Strength, Percent Strength, Size,

p.s.i. in 2 p.s.i. Millimeters 1 R.G.R. Cold 96, 000 75,000

Rolling, .470" to .141". 2 R.G.R. Anneal, 102,000 86,000 No recrys- 200 C. for 1 hr. tallization. 3 3.13. Gold Rolling, 109,000 89,000

.141 to .039. 4 R.F.Am1eal,375 62,000 35,000 0.002.

O. for 1 hr. 5 Finish Cold Rolling, 107,000 86,000

.039 to .014. 6 Finish Anneal, 67,000 30 43,000 0.002.

300 C. for 1 hr.

Application of this invention to 18% nickel-silver alloys may be readily seen by the following reference to a 0.375 thick sample having the following composition: copper, 55.8%; nickel, 17.5%; iron, 0.11%; manganese, 0.3%; lead, 0.034% with balance zinc. This alloy was cold rolled from 0.375 thickness to 0.112" comprising a R.G.R. reduction of 70% followed by an R.G.R. anneal at a temperature of 300 C. for one hour. Rolling of the ready to get ready size was continued to a RF. gauge of 0.033 thickness, a reduction of 70.5%. The metal at the ready to finish gauge was then annealed at 300 C. for one hour at temperature and again'rolled to final or finish gauge of 0.011" thickness. This third rolling reduction was 66.6% of the 0.033 inch, or a total of 97% reduction from the original gauge of 0.375. Finally the metal at finish gauge may be subjected to any subsequent heat treatment depending on the specific properties desired. The cold worked metal at finish gauge may be subjected to a heat treatment identical to the preceding anneals, specifically at 300 C. for one hour at temperature. Such treatment provides an alloy with an ultimate strength of 160,000 p.s.i., yield strength 146,000 p.s.i. with a grain size of 0.001 millimeter.

Alternately the alloy at finish gauge may also involve subjecting it to an anneal at 475 C. for one hour at temperature resulting in a tensile strength of 96,000 p.s.i., and a yield strength 88,000 p.s.i., 20% elongation with a grain size of 0.0016 millimeter.

As will be obvious, reference to grain size is employed as denoting the customary concept in the art and is expressed as the established grain size in millimeters of the most typical grain of the structure under microscopic examination. As will be understood, the estimation of grain size is expressed and determined in accordance with the procedures established by the American Society for Testing Metals.

Although the invention has been described with reference to specific embodiments, materials and details, various modifications and changes, within the scope of this invention, Will be apparent to one skilled in the art and are contemplated to be embraced within the invention.

What is claimed is:

l. A method of Working copper-base alloys comprising subjecting an alloy selected from the class consisting of copper-zinc alloys and copper-nickel-zinc alloys to at least one consecutive series of steps consisting of cold working followed by heat treating operations, said cold working operation consisting of efiecting at least a 50% reduction in the thickness of said metal and said heat treating operation consisting of a stress-relief anneal of 7 said alloy below its recrystallization temperature, and further cold working said alloy with said further cold working efiecting at least an additional 50 percent reduction in the thickness of said alloy.

2. The method of claim 1 wherein the total reduction obtained by all said reductions is between 95 and 97%.

3. The method of claim 1 comprising an additional step of subjecting said finally worked alloy to a recrystallization anneal for a sufi'icient period of time and at a temperature which heat treats that alloy without increasing the average grain size above a maximum of 0.005 millimeter.

4. The method of claim 3 including the step of further cold working the finally heat treated alloy to effect an additional reduction in thickness of at least 50%.

5. The method of claim 3 including the further step of cold working the resultant heat treated recrystallized alloy to the desired thickness and annealing said alloy.

6. The method of claim 5 wherein the last said annealing operation is recrystallization anneal for a suflicient period of time to heat treat said alloy Without increasing the average grain size above 0.001 millimeter.

7. A method of working copper-base alloys comprising subjecting an alloy selected from the class consisting of copper-zinc alloys and copper-nickel-zinc alloys to at least one consecutive series of steps consisting of cold working followed by heat treating operations, said cold working operation consisting of effecting between 50 to 70% reduction in the thickness of said alloy and said heat treating operation consisting of a stress-relief anneal below the recrystallization temperature of said alloy, and further cold working said alloy with said further cold working effecting at least an additional percent reduction in the thickness of said alloy.

8. The method of claim 7 wherein the total thickness obtained by all said reductions is between 95 and 97%.

9. The method of claim 7 comprising an additional step of subjecting the finally worked alloy to a recrystallization anneal for a sufficient period of time and at a temperature which heat treats said alloy without increasing the average grain size above a maximum of 0.005 millimeter.

10. The method of claim 9 including the step of an additional cold working of the resultant heat treated alloy to eftect an additional reduction in thickness between 50 and 11. The method of claim 9 including the step of an additional cold working the resultant heat treated recrystallized alloy to the desired thickness and annealing said alloy.

12. The method of claim 11 wherein the last said annealing operation is a recrystallization anneal for a sufficient period of time to heat treat said alloy without increasing the average grain size above 0001 millimeter.

References Cited in the file of this: atent UNITED STATES PATENTS Harrington Apr. 24, 1951 Gregory Apr. 20, 1954 OTHER REFERENCES 

1. A METHOD OF WORKING COPPER-BASE ALLOYS COMPRISING SUBJECTING AN ALLOY SELECTED FROM THE CLASS CONSISTING OF COPPER-ZINC ALLOYS AND COPPER-NICKEL-ZINC ALLOYS TO AT LEAST ONE CONSECUTIVE SERIES OF STEPS CONSISTING OF COLD WORKING FOLLOWED BY HEAT TREATING OPERATIONS, SAID COLD WORKING OPERATION CONSISTING OF EFFECTING AT LEAST A 50% REDUCTION IN THE THICKNESS OF SAID METAL AND SAID HEAT TREATING OPERATION CONSISTING OF A STRESS-RELIEF ANNEAL OF SAID ALLOY BELOW ITS RECRYSTALLIZATION TEMPERATURE, AND FURTHER COLD WORKING SAID ALLOY WITH SAID FURTHER COLD WORKING EFFECTING AT LEAST AN ADDITIONAL 50 PERCENT REDUCTION IN THE THICKNESS OF SAID ALLOY. 